Various drug delivery catheter designs and procedures have been developed over the last several years for use in a wide range of medical applications. One such design and procedure involves the delivery of therapeutic and/or diagnostic agents to a localized area of a patient's vasculature through the use of a perforated balloon catheter. Typically, such prior art drug delivery catheters include a balloon having a plurality of apertures spaced about its surface located at the distal end of the catheter. The interior of the balloon is in fluid communication with an inflation lumen which extends throughout the length of the catheter. After the balloon has been placed within the patient's vasculature or other bodily organ at the position of the treatment site, inflation fluid comprising a therapeutic or diagnostic agent is injected under pressure through the inflation lumen and into the balloon. The pressurized inflation fluid fills the balloon, migrates through the apertures in the balloon wall and penetrates the tissue wall at the treatment site. The balloon apertures are sized such that the balloon remains pressure-inflated despite the flow of the fluid agent through the apertures in the balloon wall.
Perforated balloon drug delivery catheters such as the one described above are capable of delivering a wide range of therapeutic and/or diagnostic agents. For example, perforated balloon catheters are designed for use in conjunction with angioplasty dilatation for treating the site of an opened atherosclerotic lesion or stenosis with a therapeutic agent such as heparin to inhibit unregulated smooth muscle cell proliferation and prevent restenosis. Alternatively, perforated balloon catheters may be used to deliver a drug or agent to dissolve a stenosis in an effort to avoid use of angioplasty or atherectomy procedures, or to deliver a thrombolytic agent to dissolve a clot at the lesion site. In addition, perforated balloon catheters also may be used to administer antibiotics or anesthetics directly to the treatment site prior to removal of the catheter. Other agents which may be administered through perforated balloon catheters include steroids for suppressing inflammation in a localized tissue site, anti-neoplastic for treating a tumor site, chemotherapeutics or any desired mixture of individual pharmaceuticals.
Despite the development of this broad range of applications for perforated balloon drug delivery catheters, improvement in the control of the infusion of the inflation fluid to the treatment site is desirable. Typically, the inflation fluid is manually injected into the perforated drug delivery balloon catheter by means of a syringe device comprising a syringe plunger and barrel. Accordingly, the rate of infusion of the inflation fluid to the treatment site depends on the pressure applied on the syringe plunger by the physician when expelling the inflation fluid from the syringe device. It has been found that the precise control of the pressure at which the inflation fluid is injected into the catheter is important, thus requiring great skill on the part of the administering physician. For example, the exertion of excessive pressure on the syringe plunger by the physician may result in over-pressurization of the inflation fluid within the balloon, such over-pressurization may cause high velocity jetting of the inflation fluid through the balloon apertures and possible trauma to the interior walls of the patient's vasculature.
Moreover, it has been found that the use of a pressure gauge to assist the physician in monitoring the pressure at which the inflation fluid is injected into the catheter does not assure precise control of the infusion of inflation fluid to the treatment site. For example, a drop in the pressure indicated on the pressure gauge generally causes the physician to accelerate the movement of the syringe plunger into the syringe barrel, thereby resulting in a pressure spike. Any such pressure spike may result in over-pressurization of the balloon and, consequently, possible high velocity jetting of inflation fluid through the balloon apertures.
In an effort to prevent high velocity jetting resulting from over-pressurization of the fluid within the perforated balloon, various forms of shut-off valves have been developed for limiting the pressure of the inflation fluid within the balloon. However, because these valves are designed to remain closed when the inflation fluid pressure exceeds a predetermined maximum allowable pressure, the flow of inflation fluid through the catheter to the treatment site may be discontinued for an indefinite period of time. It is understood that leaving the catheter in the patient's vasculature for any such prolonged period of time can adversely effect the patient's blood flow and thereby complicate the procedure. Moreover, the efficacy of the procedure may be compromised by a prolonged and an interrupted application of the drug to the treatment site.
Therefore, there exists a need for a method and apparatus for limiting the pressure of the inflation fluid within the perforated balloon so as to prevent high velocity jetting of the fluid through the balloon wall, and also permitting the continuous and uninterrupted flow of the drug to the treatment site.